Proceeduiqs of the 7th Internatumai WorkIng Conference on Stored-product Protection - Volume 2

Application of PLC and SCADA in auto-control systems forsilo grain handling

Zhang Yaozu and LIU Hong!

Introduction

Vertical silo fmds ItS great favors in the field of gram,feeds, foodstuff and light mdustnes because of ItScharactenstics of high mecharuzation, large capacity, quickcirculauon, less area occupation, etc Nowadays, concreteand steel plated silos are widely used for gram storage, andthe SIlo storage m proportion to general capacity of Chmagram depot IS annually mcreasedTo realize silo mechanization operation, the electnfication

and auto-control systems are absolutely necessary for thecoordmated control over the vanous gram handlmgequipment of conveymg, cleanmg, weighmg , ventilatmgand dust-removing HIgh-reliable PLC IS specificallydesigned for mdustnal control This PLC ensures 20-yearcontmuous normal operation Without mistakes Its msertedmodule IS exchangeable withm a few minutes, m case ofhardware failure due to any accident,Instead of traditional mImIC panel and operation desk,

man-machme mterface IS adopted All operational functionsare carried out by SCADA user's operation and momtonngconfiguration mterface based on the micro-computer underthe condinon of Wmdows. Computer configuration man-machme mterface makes the features of direct SIght,dynamic display and user's fnendlmess.

Brief introduction of silo process

Shanghai Mechanization Gram Depot bears the responsibilityof receivmg , dispatchmg , intermediate transportation andstorage of free flow bulk gram, mamly wheat and maize.The technological design IS m focus on 35,000- ton silo andItS workmg tower IS mtegrated WIth full production lme offlat warehouse, speCIfIC raIlway and 10,000t-grade wharfThIS concrete vertical sllo IS composed of 33 bms mcludmg

21 SIlos (m 3 parallel rows WIth 7 sllos each) and 12 starsllos. ThIS SIlo IS of 9m ID WIth gram stackmg heIght of29 .Sm The workmg tower IS 9-storeyed structure bmldmg200tlh wharf eqmpment for m-takmg gram from

waterway: the commg gram IS to be put mto the sllo when It

1 Shanghm Zhenda Storage Industry and Commerce Company,Shanghm, P R Chma

IS conveyed, pre-cleaned and weighed by two 200tlh-production lmes m the workmg tower, and/or to be sent torail wagon directly or to be packed m flat warehouse forstorage Aspirator for dust-removal system IS equipped atthe places where gram gravity-drop difference occurs on theprocessmg route.200Uh equipment such as 2 sets of scales, a pre-cleaner,

bel t conveyors, en-masse cham conveyors and eleva tors aremstalled m the workmg tower to fulfill the functionaloperations of m-takmg , pre-cleanmg , weighmg , re-circulatmg from bm to bm and out-taking

Functional system

All equipment on production lme are auto-controlled andmterlocked by PLC Dunng normal operation, theseequipment are to be turned on respectively m an order ofconversed process flow and to be turned off in an order ofprocess flow. At the time when failure occurs, computermakes ItS solutions by alarmmg , sequential stop, emergencystop and completely mstantaneous stop respectively on thebaSIS of failure condition An mtegration of central controland local SWItch, automatic and manual modes are adoptedfor convemence of mamtenance operation System process ISSImultaneously displayed by the computer

Start-up, stop of the interlocking equipmentaccording to technological flow

In addition to conveyors, weighing machmes, and pre-cleaner, the SIlo m Shanghai Gram Depot No.7 IS equippedWIth dust-removal system and magnetic separator to meetthe technological requirement for large-sized silo operation,electncal protection and anti-explosion safety measures. Toput productiOn lme mto operatiOn, dust-removal systemshould be turned on at the very begmmng, then the otherrelevant eqmpment be turned on respectively m an order ofprocess counter-flow. All mvolved eqmpment WIll be stoppedrespectively m an order of process flow and the dust removalsystem be stopped at the end, whlle 'stop operatiOn button'IS pressed. At the time when fallure occurs, the eqmpmentfrom source to the faulty eqmpment WIll be stoppedImmedIately and the dust removal system wlll also bestopped then.

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Proceedsnqs of the 7 th International Working Conference on Stored-product Protection - Volume 2

Route auto-selection and start-up/stop equipmentaccording to the selected silo bins

The process control can be divided mto 8 divisionscontammg more than 20 processing operations A main localmanual control/stop / remote control selection switch ISlocated m a central control room (CCR) to prevent localswitch from random operation. Each equipment has ItSmanual mamtenance / stop / remote selection switch PLCcontrols the operation from the control room, when remoteposition is selected. And local manual switch IS positioned at'start-up / stop' for equipment maintenance and testingSeveral emergency push- buttons are equipped on each floorof the working tower m order to stop all involvedequipment, If necessary. Complete control system possesseswith 3 sub-systems: CCR manual operation, automaticoperation and simulation Manual operation from CCR - eachequipment can be started-up / stopped easily as a separatedunit, Computer screen displays all mspection signals andequipment real-time status. There's no mterlockmg betweenany other process equipment Automatic operation - whenprocess selection, bin selection, confirmation and start-upare made, dust removal system WIll automatically be runnmgand the related equipment Will also be runrung sequentiallym an order of process counter-flow m comphance With therequirement of the selected operation route. SImulation ISfor the purpose of trammg and exlubition.Each sub-system owns 6 flow-processes such as gram

intake, outtake, re-circulate from bm to bm, deliver intoflat warehouse directly, dispatch to flat warehouse,synchronous operation of intake and outtake from silo towarehouse. Route selection can be done freely and easily.What the operator should do is Just to choose bms, confirmand activate by the mouse on the condition of determmedoperation route.

emergency button on the display according to the situation offaulty equipment

Silo management system for real-time inventorycontrol

ThIS functional design IS presented by real-time inventorydisplay of both upgraded data of the handled or remainedproducts (gram) in silo and SImulation of the level changesof the products in silo based on the weighing -informationfrom auto-scales and computer conversion.

System formation

The silo remote control system m Shanghai Gram Depot No.7 consists a set of COMPAQ486-66 computer as the SCADAworkstation, a power source cabinet, a PLC cabinet with apower distnbutor , MCC cabmet for control of 10 motors, 2large-screen displays of 37 and 20 inches, a 5 kVA isolatedtransformer, 3 sets of 1kVA on-lme UPS. Amencan Allen-Bradley PLC-5125 cor troller consisting of a mam rack and 3expanded racks IS installed into a PLC cabmetIn this automatic control system Senes 486 mdustnal

micro-computer manages bulk gram handling m the silos,while PLC controller fulfill auto-control over the equipmentoperation. It IS equipped With the process SImulation todisplay equipment real-time status and to send both VIdeoand audio alarms promptly when failure operation happens tothe equipment And the mstallation of local manual switchesIS additionally satisfied for the system requirements ofrehabihty, visuahzation and applicability.

System hardware architecture

PLC IS used for operation control over the equipment incomphance With process demand. PLC commumcates WithSCADA, equipment status can be real-time reflected bySCADA and the instructions from SCADA can be real-timeresponded.

Auto-switch and thermo-relay for electrical control system Senes PLC-5 programmable controller produced byare to keep the equipment from short-circuit and Amencan ALLEN-BRADLEY Co. IS utilized for the PLCoverloading. Speed sensor and belt misahgnment switch are I/O module is of msertable module structure HardwareeqUlpped on each elevator. Matenal block sWItches are failure can be resolved WIthin a few mmutes. AvaIlablemounted on each honzontal conveyor. Level sensors are set quantity of separated I/O ranges from 16 to 3072 pomtsup onto each sIlo bm And manual/automatic dIversIOn Estimated I/O points m ShanghaI Gram Depot No.7 areswitches for start / stop of the equipment are mstalled at about 1120, and the virtual I/O points are decreased to 928each story m workmg tower. All sIgnal information from on- because of our optimIzed deSIgn. So this PLC 5125 type PLCSIte sensors are transmitted by PLC mput / output With max Supporting 1024 I/O pomts are adopted for themterfaces, MCC cabmet operates mvolved eqUlpment This system.technology reaches the hIgher automation level. PLC 5125 is a large capaCIty programmable controllerThIS safe and reliable system ensures the dIsplay of the from PLC-5 senes. Its module structure and standard

equipment real-time status and ItS auto-solution for all hardware techmque can be randomly arranged accordmg tooperations, and let the operator make manual emergency the detaIled needs. This PLC has maXImum 21K memory,stop operation by pressmg on-SIte emergency button and EPR0M13K, selectable 1024 I/O points, 8 racks mcluding

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Automatic resolution of alarming, sequential stop,emergency stop on the basis of equipment failure

Proceedmqe of the 7th International Wm-kmg Conference on Stored-product Protection. - Volume 2

one local rack and 7 remote racks, commumcation interfacemcluding DR + and remote I/O interfaces. Executive timefor program scannmg IS 8ms/1K bit. Available forconnection With various modules of PLC-5 senes, forcommunication With multi-networks through DH-PLUSnetwork, for user's program and testing With ladderdiagram, words entry and flow process of system functionalcontrol.

System software design

SCADA configuration control takes configurationoperation interface as man-machine dialogueinterface

Configuration momtonng software IS In Touch Version5.0 from Amencan Wonderware Co. All functionaloperations are carried out by In Touch user's operation andmomtonng configuration interface based on a set of 486micro-computer under the condition of Windows Traditionalmimic panel and operation desk are omittedThe In Touch charactenstics are as follows:• The point number and max configurationdemonstration momtored by the In Touch software areof no hrrntation , because of the capacity Windows 3.0management memory and the expanded storage space

• Perfect configuration function and VIvid display· Vanous alarnung measures of digital alarm, ratio alarm,dIfference alarm, etc.

• Functional conversion for 11 database• 4 real-time curving diagrams, 4 profile trend curves andalarming indications play the role of on-lme mstructionfor the operator.· Multi-modes for user data mput· Flexi.ble configuration.The user can establish configuration and version displays

by operating the simple stnpes, sealed configurations,words and figures or the comprehensive pagers of alarm,position, trend, combination and totalised drawings

Parametric definition

1) Design of configuration control and operation interface

Year In-taking Out-taking

3,634t

11 ,978t

4,998t

1995

1996

1997

23,331t

24,655t

408t

Dunng 3-year-operatIon, overall control system IS in goodorder, Without failure. It IS well accepted by the usersbecause of ItS fnendly man-machine interface, simphfied

Configuration mterface can be divided mto followingthree parts:· Automatic mterlockmg control· Manual control· Mimic Simulation

2) Parametric defmition of configuration drawing andinterface7 mam configurations and some ancillary configurationsfor route selection and confirmation are drawn mcompliance With the technological requirements ofgram m-takmg , out-taking and re-circulatmg from bmto bin. Image display IS made by easy operationInterface parametnc defnution IS to estabhsh therelationship and to change the color, shape and Size,depending on the status of PLC I/O point and therelevant dynamic configuration

Communication between Britain SIMON electronicscale and PC SCADA

The data from electromc scale can be dynamicallydisplayed on PC computer by the communication, and theinventory can also be reported Simultaneously Thepatterned communication agreement between SIMON scaleand PC computer IS exclusive Our project engineers havemade out the explanation of this commumcation agreementthrough hard-connection of scale and computer and repeatedtesting and analyzing m light of only one page words fromSIMOM manuals. Based on the achieved communicationagreement, DDE Server I/O interface dnve modules arecompiled for In Touch configuration momtonng software.Thus, the measured data from electronic scale can bereflected on the configuration display, the height of grainlevel in each bin can be Simultaneously shown via computercalculation, and the inventory can be reported respectively.

Production check

The comrrussionmg and trial operation of this system hadbeen Implemented by the Spnng Festival m 1995, and loadof silo gram ballast (mainly wheat) and large-scale input hadbegun since then:

Recirculatmg Packing

17,750t 6677

25,660t 8,986t

17,765t 6,230t

easy-understanding operation mstructions and completealarming system for equipment failure.

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Proceeduuje of the 7th International Workmg Conference OIl Stored-product Protection - Volume 2

Conclusion

ThIS system gams the following advantages:2-grade management system IS adopted and computer

comprehensive management system IS estabhshed. Thanksto PLC for its large reduction m quantity of mediate-relayand hard-wmng , the rehabihty and flexibihty of the systemare greatly enhancedThis system IS suitable not only for the requirement of SIlo

control, but also for the other mdustnal requirements ofprocess operations of nee null, flour rmll , feed null, 011refiner, foodstuff factory and etc.. And the system is nowcontributed to the project of Zhengzhou Mechanization GramDepot, World Bank Projects of Liuzhou Intermediate GramDepot and Chenglmgji Intermediate Gram Depot.Smce the system IS put into operation, It has played an

Important role m speeding up harbour transportation.

Thanks to the comprehensive functions of monitoring andcontrollmg, matenal blockage and equipment stoppage arelargely decreased, labour strength IS greatly reduced and themanagement IS also updated to the further high levelBased on the replacement of tradmonal control desk and

mImIC panel with computer configuration control andoperation interface, this system features: direct digitalcontrol, high mterference-free ability, absolute rehabihtyand less dimension All working operations can be realizedby optirmzmg selection of process route direction accordingto technological demands. And the smart operations for auto-alarm, sequent and emergent stop are created.The application of this system reduces the labour

strength, avoids mharmoruous operation lmks and delaysresolution for removal of equipment failure , decreasesmistakes or errors, provides the technological environmentfor upgrade of equipment utihzation ratio, labourproductivity and capability of gram handling

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